1. Field of the Invention
The present invention relates to a novel polymerizable ultraviolet absorber, which is water-soluble or alcohol-soluble, and also discloses a method for preparing the same and application thereof in the fields of medical optics.
2. Description of Related Art
Ultraviolet rays in sunlight radiating on the Earth mostly have radiant energy of the wavelength between 290 and 400 nm. In general, ultraviolet rays can be absorbed by the thermosphere at about 100 km above the Earth's atmosphere if their wavelength is less than 175 nm, and can be absorbed by the ozonosphere at about 15 km above sea level if their wavelength is in the range of from 175 to 290 nm. As well-known, exposure under ultraviolet rays will cause skin and cornea injuries and result in visual impairment, and also is a main cause of cataracts. Hence, it is important to learn how to sufficiently provide visional protection from ultraviolet rays, how to decrease morbidity of cataract, and how to protect UV-susceptible people such as patients treated with ophthalmic surgery or light-sensitive patients.
Generally, ultraviolet absorbers can be added in the composition of contact lenses or common spectacles to absorb ultraviolet rays of from 290 to 400 nm. Hence, harmful radiation effects of ultraviolet rays can be lowered so as to protect the visional system and to reduce the morbidity of cataract. Up to the present, there has been developed various ultraviolet absorbers, and those are efficiently applied in the composition of contact lenses or common spectacles. However, in order to prevent loss of ultraviolet absorbers from lenses in any condition, the material of the lenses preferably is grafted or copolymerized with polymerizable ultraviolet absorbers. For example, U.S. Pat. No. 4,304,895 discloses reactive ultraviolet absorbers for contact lenses, which are represented by the following formulas.
Although the abovementioned ultraviolet absorbers of diphenylmethanone having reactive groups can participate in polymerization, this kind of ultraviolet absorbers has inadequate stability. When the abovementioned absorbers are applied in lenses, the ultraviolet resistance thereof decreases gradually during storage of the lenses or due to the lifespan thereof. Meanwhile, the abovementioned ultraviolet absorbers are insoluble in hydrophilic polymerizable comonomers and copolymers of acrylate owing to their hydrophobicity. Even though they are slightly soluble in hydrophilic polymerizable comonomers and copolymers, they trend towards aggregation from microphase separation when copolymers undergo hydration. The aggregation makes lenses appear misty and hence reduces transparency of lenses.
Furthermore, U.S. Pat. No. 4,528,311 discloses a reactive ultraviolet absorber represented by the following formula.
Although the foregoing ultraviolet absorber of benzotriazole is polymerizable and has preferred stability, this compound is still hydrophobic. Such hydrophobicity will result in occurrence of microphase separation and mist.
Furthermore, U.S. Pat. No. 6,036,891 discloses an ultraviolet absorber which is made by reacting a new compound, 2-(2′-hydroxy-5′-hydroxyethoxyethyl-phenyl-2H-benzotriazole, with methacryloyl chloride to form a monoester compound. This compound is represented by the following formula.
However, it is unfortunate that the specification of the above-mentioned patent discloses neither how to obtain 2-(2′-hydroxy-5′-hydroxyethoxyethyl-phenyl-2H-benzotriazole nor how to synthesize it. Moreover, although this reactive ultraviolet absorber is more hydrophilic than those synthesized in the past, its water solubility is still poor. Besides, an ultraviolet absorber, disclosed in Japan patent no. 3,655,061, represented by the following formula also has the problem of poor solubility.

Hydrophilicity is a property different from water or alcohol solubility. Materials for manufacturing contact lenses should have good hydrophilicity so that the contact lenses can move in accordance with eyeballs to achieve rectification of eyesight. Besides, sufficient hydrophilicity can increase comfort of contact lenses. Because hydrophilicity is important to contact lenses or intraocular lenses, materials for manufacturing those lenses are required to be hydrophilic. In addition, a little amount of nonreactive components should be removed by washing to ensure no toxicity exists after synthetic reactions. Generally, residual nonreactive monomers need to be removed by use of a great deal of solvents in a manufacturing process. However, this not only requires a lot of time and work, it also increases costs. If components used in synthetic reactions are water-soluble or alcohol-soluble, neither mist is generated after polymerization nor volatile organic compound is discharged while residual nonreactive monomers are removed by washing. Hence, problems to the environment do not occur, and production costs can be reduced.